The present invention relates generally to contact lenses and, more particularly, to a contact lens for the eye of a patient with keratoconus disease and to a method of making such a contact lens.
Keratoconus is a progressive disease of the cornea which often results in an outward protrusion of the central area of the cornea, causing a thinning and disfigurement of the central cornea tissue. Since the cornea is basically a refracting surface for light rays received from the atmosphere, if the cornea is diseased with keratoconus, the resulting protrusion or cone distorts the normal refracting of the light rays causing poor visual acuity and distortion. In addition, keratoconus is often very painful and irritable for the patient.
There are two known basic techniques which may be used to control or correct keratoconus. The first, more drastic technique involves the patient undergoing a surgical corneal transplant. The second, more conventional technique is to fit the patient with a special contact lens having a back or posterior surface which is specifically designed to permit the diseased portion of the cornea to conform itself to the lens surface, resulting in both control of the keratoconus disease and improved visual acuity. Obviously, if the disease can be successfully controlled or corrected using such a special contact lens, a surgical corneal transplant can be avoided.
In the past, keratoconus patients were fitted with large, bulky scleral impression form contact lenses. The large scleral lenses, which fit over the whole cornea and the entire bulb of the eye, were quite uncomfortable to the patient in that they generally fit too close to the protruding cone area therey irritating the cornea. In addition, visual acuity with the large scleral lenses remained relatively poor.
More recently, smaller, corneal contact lenses have been employed for the fitting of patients having keratoconus disease. Initially, the smaller corneal contact lenses were approximately eleven millimeters in diameter and included a variety of peripheral curves. Such early corneal contact lenses attempted to maintain a three point contact with the eye, touching the central corneal tissue where the cornea protruded as well as the normal tissue in as many meridians as possible. These lenses generally put too much or too little pressure on the corneal cone and often resulted in corneal swelling. In some cases such lenses actually worsened the disease.
A new design contact lens has recently emerged for patients having keratoconus disease. The new design lens, called the Soper cone, includes a central area having a single central radius of curvature which permits the lens to bridge or "vault" the diseased area of the cornea and a single flatter peripheral area to provide a bearing surface for engaging the healthy area of the cornea. A relatively sharp demarcation exists between the two areas of the Soper cone lens. Although the Soper cone lens has produced relatively good results, it still provides a three point contact system which results in the application of too much or too little pressure to both the diseased and non-diseased areas of the cornea. In addition, the Soper cone lens results in irritation to the patient due to the sharp demarcations between the two areas which produce irregularities in the lacrimal system due to the passage of too much or too little fluid between the two areas of the lens. The lens also does not improve visual consistently.
The present invention provides an improved contact lens for the eye of a patient with keratoconus disease and a method for making such a lens, which provides better control of the diseased, thinned area of the cornea and more consistency in visual acuity while causing the patient less irritation than with the prior art lenses. The lens of the present invention does not actually contact the cornea. Rather, it relies on fluid compression caused by the differential pressure of the atomosphere outside of the eye and the space between the lens and the eye to maintain a thin layer of tears to cushion the lens from the surface of the cornea.